Low power devices that operate from a battery or from power harvested from an environment generate a low current or voltage to prolong the device operation. A boost converter can generate an output voltage that is higher than its input voltage given a low input voltage or current, and in this way the low power devices can harvest energy from a low input. When the input voltage is very low, however, offsets in the circuit of the boost converter can make the small input voltage hard to be detected and used accurately, and mismatch inside the boost converter can lead to significant variance such that a logic level of an output of a gate component is altered, and thus cause an inaccurate output voltage from the boost converter.
Various ambient sources can be used for harvesting energy, including light, vibration, thermal, and radio frequency. Energy harvesting can be implemented from outdoor sun-light. Usually, these energy harvesters are relatively large in size. They can be used to harvest large amount of power (in kWs) at high voltages. These energy harvesters can achieve high efficiency with very good maximum power point tracking. In contrast, micro-power energy harvesters using solar cell include wireless sensor networks (WSN) or Bluetooth sensor networks (BSN) energy harvesters. These can be used for low power systems. Usually, they are small in size and harvest very low amounts of energy (in pWs) due to the smaller size of solar cells and low ambient light associated with the indoor lighting condition. Another energy harvester that is commonly used for BSN application is a piezoelectric harvester, which harvests mechanical energy from vibration. These energy harvesters can harvest 10-100's of μW of available power. Electrical energy is generated when mechanical stress is applied on a piezoelectric material. Recently, piezoelectric harvesters suitable for BSNs have been demonstrated. These harvesters can harvest output power of few μW to 100's of μW at efficiencies above 80%. Harvesting energy from available RF power is another means of obtaining energy for BSNs, which can supply enough energy to power BSNs.